Process for the manufacture of chlorine dioxide



PRGCESS FOR THE MANUFACTURE OF CHLORINE DIOXIDE Rudolf Hirsehherg, Franldfurt ain Main, Germany,

assignor to Farbwerke Hoechst 'Aktiengesellsch'ait,

The reaction according toEquation 1 leads to the desired chlorine dioxide whereas the reaction according to Equation 2 takes place as undesired side-reaction. The higher the proportion of Reaction 2 in the total reaction, the lower the yield of chlorine dioxide and the higher the consumption of hydrochloric acid and the production of chlorine. Even arelatively low proportion of Reaction 2 in the total reaction considerably increases theconsun ptionof hydrochloric acid and contaminates the chlorine United States Patent dioxide formed with high amounts of chlorine. This fact is particularly disadvantageouswhen the chlorine dioxide produced is intended for use in the manufacture of sodium chlorite, in which case the accompanying chlorine must be separated. The smaller the amount of chlorine carried along by the chlorine dioxide, the easier will be the separation of chlorine dioxide and chlorine. For a rational manufacture of chlorine dioxide by reducing, for example, sodium or calcium chlorate with hydrochloric acid, it is there-fore important to keep the proportion of the undesired'Side-Reaction 2 in the total reaction as low as possible.

A known process for the manufacture of chlorine dioxide consists intransforming an aqueous suspension of calcium hydroxide into a solution of calcium chlorate by treating it with gaseous chlorine and then reacting the solution of calcium chlorate with hydrochloric acid to obtain chlorine dioxide and chlorine. In the most favorable case, however, yields of chlorine dioxide of 80% are obtained, calculated on the chlorateused, while the resi- :HCl are required per mol of chlorine dioxide formed,

while according to Equation 1 only 2.0 mols H01 would be necessary per mol chlorine dioxide.

dual 20% react according to Equation 2 with the sole The proportions of Reactions 1 and 2 in the total reac- 7 tion are not constant in the course of the reaction; at the beginning especially the reaction according to Equation 1 takes place, whereas at the end, when the reaction solution only contains little chlorate,v the reaction mainly takes place as indicated in Equation 2.- Some known processes make use of this phenomenon. They are carried out in a manner such that only part, for example -80% and not the total'amount, of the chlorate first introduced into the reaction vessel is reacted with hydrochloric acid. The

V unexhausted chlorate solution is then removed from the reaction vessel and either abandoned or freed from the chloride formed by crystallization processes, concentrated, again admixed with fresh chlorate and reconducted into the reaction vessel; Furthermore, processes are known amounts to 76.1%.

3 ,101,253 Patented Aug. 20, 1963 7 example sulfuric acid, prior to the addition of hydrochloric acid or a chloride.

In this manner it is possible to increase the proportion of Reaction :1 to -94% of the total reaction and to repress the formation of chlorine in favor of that of chlorine dioxide. However, the disadvantage of said known processes 'resides in the fact that either a loss of chlorate 0ccurs by abandoning part of the chlorate used orv that they require extensive and partially expensive auxiliary devices such as electrolysis, coolingand vacuum installations, and complicated processes, such as crystallizations and concentrations. The processes carried out with reconduction of the chlorate furthermore involve the disadvantage that the calcium chlorate obtained by an economical process from calcium hydroxide and chlorine cannot be used and that the chlorine necessarily formed cannot be utilized again in the process. The processes carried out with the addition of a non oxidizable acid possess the disadvantage that only chloride-free chlorate can he used and that calcium chlorate which has been produced, for example, from chlorine and calcium hydroxide is unsuitable on account of its high chloride content. Moreover, in said known processes an additional acid is required, for example sulfuric acid. p

The present invention provides a process for the manufiacture of chlorine dioxide by reducing alkali metal or alkaline earth metal chlorates with hydrochloric acid in aqueous solution, wherein the reaction between chlorate and hydrochloric acid is carried out in the presence of manganese and/or, silver ions. The reaction is suitably carried out at a temperaturein the, range from 0 to C. and preferably from about 20 to about 70 C.

The process of the invention avoids the disadvantages of the known processes and gives a high yield of chlorine dioxide.

The process of the invention can be carried out, for example, in a manner such that the reaction solution is admixed with manganese chloride, for example MnCl .4H O, manganese dioxide, silver nitrate, silver oxide or silver chloride so as'toproduce the manganese and/or silver ions. Especially suitable are concentrations of 0.5-1.5 g.

Mn+ ions per liter of reaction solution or 005-0. g. Ag+ ions per liter of reaction solution, concentrations outside said ranges being likewise possible. It has been found, for example, that with a complete reaction of the chlorate used with hydrochloric acid, a chlorine dioxide yield of about 95.3%, calculated on the chlorate, can be obtained using a calcium chlorate solution of about 0.65 mol Ca(Cl0 per liter, produced by chlorinating an aqueous suspension of lime and containing 0.55 g. Mn ions per liter. The molar proportion Cl :ClO in the gas mixture produced is 0.636. As compared therewith, a yield of 78.7% only and a proportion of Cl :ClO of 1.29 are obtained under otherwise identical conditions but in the absence of manganese ions. The presence of silver ions has the samefavorable effect. When, forexarnple,

0.216 g. Ag+ ions are present per liter of reaction sol-ution,a chlorine dioxide yield of 93.7% is obtained with a complete reaction of the chlorate usedwith hydrochloric acid, whereas in the absence of silver ions the yield obtained under otherwise identical conditions only The catalytic activity of small additions ofmanganese ions, for example, in the form of MnC1 .4H O, diminishes as the reaction temperature decreases. It is therefore suitable to operate in the presence of manganese ions at a temperature above 35 C. The activity of silver ions is relatively independent of the temperature of the reaction solution.

A practical activity of manganese 10118 at low temperatures can be obtained by adding small amounts of silver ions to the reaction solution containing manganese ions.

In this case amounts of silver ions are sufficient which, when used alone, would not yet have a strong action. For example, at a reaction temperature in the range from 16 to 19 (land in the presence of 1.39 g. Mn ions per liter of reaction solution of calcium chlorate, *a yield of chlorine dioxide of 80.3%, calculated on the chlorate,

is obtained with a complete reaction of the chlorate with hydrochloric acid. When, however, 0.021 g. A g ions,

for example in the form of silver nitrate, are added per "liter of reaction solution, the yield is increased to 91.5% under otherwise identical conditions.

As compared with the known processes, the process of the invention represents a considerable advance since it "permits reaction of the total amount of chlorate used in one reaction stage in a relatively simple manner and with a high yield of chlorine dioxide. The same or even higher yields are obtained than in processes in which the chlorate is only partially reacted and the unexhausted reaction solution is worked up, and which require addi- 'tionalexpensive enrichment steps. A further advantage of the process of the invention resides in the fact that the reaction between the chlorate and hydrochloric acid can be carried out at convenient temperatures, preferably "in the rangefrom 20 to 70 C. In contradistinction there- 'to,rnost of the known processes are realized either at very "low or at relatively high temperatures, for example at about 15 C. or at about +100 C., which, especially in the latter case, may involve difficulties on account of "the high thermal instability of chlorine dioxide and the corrosive nature of the gases formed and the reaction J solution. When a calcium chlorate/ calcium chloride solu- 'tion is used, as obtained in the chlorination of lime suspensions, the practically pure calcium chloride solution leaving the process furthermore represents a valuable byproduct. If necessary, it can be freed without difiiculty from the small amounts of catalyst contained therein, for example by a'treatment with a smallexcess of lime and air.

For carrying out the process of the invention, in addition to calcium chlorate solutions obtained by chlorinating lime, other chlorates can be used with the same success,

for-example sodium chlorate or potassium chlorate or also chloride-free calcium chlorate solutions. case it is of special advantage to add to the reaction solution, prior to the reaction, chloride ions, such as sodium In this chloride or calcium chloride, approximately in a proportion of 0.5 to mols chloride ions per mol of chlorate Fused.

The hydrochloric acid required for reducing the chlorate can be added to the solution in the form of aqueous hydrochloric acid or gaseous'hydrogen chloride. Alternatively, the hydrochloric acid can be produced in situ in thereaction solution, for example, by adding a sodium chloride solution to a solution of chlorate in a non reducing acid, such as sulfuric acid, in the presence of manganese and/or silver ions. The process of the invention can furthermore be carriedout by reacting hydro- The tinuously or continuously. On account of the considerably higher yields at low concentrations, as compared with a process using catalyst-free solutions, it is of special advantage to carry out the process of the invention in continuous manner.

The process of US. Patent 2,172,434 in which an aque- '=ouss01ution of manganese chlorate is subjected at high temperatures to a disproportionation toyield chlorine dioxide and manganese dioxide does not suggest the process of the present invention. In that patent manganese dioxide is separated and then reacted with hydrochloric acid to yield manganese chloride and chlorine. The characteristic feature of said known process consists in that several stages are'required and that: the molar ratio of manganese to chlorate is 132. Thebivalent manganese used acts as reducing agent and must be regenerated in a second stage. The amounts of manganese required per mol of chlorine, dioxide are so large that an abandonment of the manganese in the exhausted reaction solution is notadmissible from an economical point of -view. Incontradistinctionthereto the process of the invention is carried out in onestage, wherein hydrochloric acid is the reducing agent while 'the manganese and/or silver ions added catalytically accelerate and control the reaction between the reactants. The process of the invention can be carried out at low temperatures and the molar amounts ofmanganese or' silver are smaller than 1% of the 'molar amount of chlorate used. Therefore, they must not be recovered without considerable economical disadvantages occurring.

The following examples serve to illustrate the invention, but they are not intended to limit it thereto.

vExample .1

'vessel-was'introduced into an aqueous sodium peroxide solution in order to determine in usual manner the amounts of gas produced. The reaction being terminated -thesolution contained 562.5 grams NaClO and 462.5 grams NaCl. The yied' of chlorine dioxide, calculated on the chlorate used, was 95.3% and'the molar ratio of chlorine to chlorine dioxide in .:the.-gas.produced was Example 2 The experiment was carried out as described in Example 1 with the exception that no manganese chloride was added. .The reaction lasted for 9.6 hours and 2.08

liters HCl (10 N) were required. The chlorine dioxide yield amounted to 78.7% and the molar ratio of chlorine to chlorine dioxide was 1.3:1.

Example 3 5 liters of a solution, prepared as described in Example 1, of 138 grams Ca(ClO and 385 grams CaCl per liter'were admixed in a reaction vessel with cc. of a N AgNO solution (0.216 gram Ag+ per liter of reaction solution; Ag ":ClO ==0.0015 :1) and then treated within 2.17 hours with atotalamount of 1.74 liters HCl (10 N).

The reaction temperature was 70 C.; for diluting the gases formed 2.2 m. airwere blown into the reaction solution per hour. vessel charged'with sodium peroxide solution contained at the end of the reaction 565 grams NaClO and 498.5 grams NaCl. The yield of chlorine dioxide, calculated on the chlorate used, amounted to 93.7% and the molar 'ratio of chlorine to chlorine-dioxide was 0.68211.

Example 4 The absorption 5 liters HCl (10 N) were. required. The yield of chlorine dioxide was 76.1% and the ratio of Cl :ClO was 1.36:1.

Example 5 10 grams MnCl .4H O (0.55 gram Mn /Iiterreaction solution; Mn+ :ClO =0.0079:1) were added to 5 liters of an aqueous solution of sodium chlorate containing per liter 135.0 grams NaClO and the solution was III. The solution leaving vessel III was purged with air reacted in a reaction vessel at a temperature of 70 C.

within 11.25 hours with a total amount of 2.34 liters HCl 10 N) while simultaneously passing through 1.1 m. air per hour. The gases formed were introduced into an absorption vessel charged with sodium peroxide solution which contained at the end of the reaction 521 grams NaClO and 539 grams NaCl. The chlorine dioxide yield, calculated on the chlorate usedywas 90.9% and the molar ratio Cl :ClO was 0.8:1.

Example 6 Example 7 5 liters of a solution prepared as described in Exampics 1 and 3 and containing per liter 138 grams Ca(ClO and 385 grams CaCl were admixed in a reaction vessel with 25 grams :MnCl- .4H O (1.375 grams MnW/liter reaction solution; Mn+ ClO -=0.0l88:l) and 25 cc. N silver nitrate solution (0.054 gram Ag+/liter reaction solution; Ag+:ClO =0.O00376:1) andtheu atotal amount of 1.99 liters HCl (10 N) were added in the course of 2.7 hours at a temperature of 40 C. In order to dilute the gases formed 2.2 m. air were blown per hour into the reaction solution. The gases produced were determined as described above by reacting them with a sodium peroxide solution. grams NaCl were obtained. The chlorine dioxide yield, calculated on the chlorate used, amounted to 94.8%. The molar ratio Cl zclo 'was 0.667z1.

Example '8 The experiment was carried out as. described in Example 7 with the exception that no silver and manganese ions were added to the reaction solution. The reaction lasted for 3.6 hours, 2.6 liters HCl 10 N) wererequired. The chlorine dioxide yield was 79.9% and the molar ratio Cl zClO was 1.25:1.

Example 9 5 liters of asolution prepared as described in Examples 1, 3 and 7 and containing per liter 139 grams Ca(ClO and 387grams CaCl were admixed in a reaction vessel with 25 grams MnCl .4H O (1.375 grams Mn+ /liter reaction solution; Mn+ :ClO -=:0l87:1) and 10 co. N AgNO solution (0 .0216 gram Ag+/liter reaction solution; Ag- :ClO -=0.000l :1) and the whole was treated for 3.73 hours with 2.86 liters HCl N) at a reaction temperature of 17-19 C. For diluting the gases formed 2.2 m5 air were blown per hour into the reaction solution. The amounts of gases produced were determined as described above by reacting them with sodium peroxide solution. 556 grams NaClO and 558 grams NaCl were obtained. The yield of chlorine dioxide corre-v sponded to 91.5%, calculated on the chlorate used, and the molar ratio 015C10 was 0.777: 1.

Example 10 The experiment was carried out as described in Example 9 but without the addition of silver ions. The reaction lasted for 4.0 hours and 3.1 liters HCl (10 N) were required. On account of the low reaction tempera.- ture a yield of only 80.3% was obtained; the molar ratio Cl :ClO was 1.24:1.

572 grams NaClO and'493 I 'countercurrent with the chlorate solution through the in a vessel IV (capacity about- 1.5v liters) and discharged via a siphon. I

The reaction liquid in vessels I-IV had a temperature of. 71 C'., 73 C., 76' C. and 74 C., respectively. Vessel I was charged per hour in doses with 2.36 liters calcium chlorate solution prepared in known manner by chlor-inating an aqueous suspension of calcium hydroxide and containing about 149 grams Ca(ClO and 416 grarnsCaCl per liter. Simultaneously about 0.12 liter of a catalyst solution was introduced per hour containing per liter 100 grams MnCl .4-H O, 40 cc. N AgNO solution, 160 grams CaCl and 10 cc. concentrated HCl (in oader to maintain the silver in solution as complex compound). By means of gas distribution devices 1.3, 0.8, 0.8 and 0.1 cubic meter, respectively, of air were blown per hour into reaction liquids in vessels l-IV, which air was each time admixed with gaseous hydrogen chloride (except for the air introduced in vessel IV) so that the chlorate concentrations amounted in vessel 1 to about 45-48 grams/liter, in vessel II to about 1213 grams/liter and in vessel Ill to about 2-4 grams/liter Ca(ClCO The air blown into vessels I-IV was conducted in vessels and then introduced into sodium peroxide solution in order to determine the chlorine dioxide yield in known manner. In thecourse of3 hours- 819 grams. NaClO corresponding to a yield of 89% calculated on the chlorate used, and 786 grams NaCl were obtained. The molar proportion of Cl :C1O in the gas was 0.742i 1.

Example 12 I The experiment was carried out as described in Example -11, but without the addition of catalyst solution. In the course of 3 hours 579 grams NaClO corresponding to a yield of chlorine dioxide of 62.7% calculated on the chlorate used, and 1.448 grams NaCl were obtained.

The molar proportion Cl :ClO in the gaswas 1.94:1.

- Example 13 tion containing '554 grams NaClO per liter, 477 cc. H 50 of 78% strength) and 1.134 liters of a solution containing 321.5 grams NaCl and 10 grams MnSO H O per liter.

For diluting the chlorine dioxideformed 1.5 cubic meters air were blown per hour into the reaction liquid.- The excess reaction solution flowing off was purged with 0.3 cubic meter air per hour in a second vessel having a capacity of about 3 liters of liquid, and discharged via a siphon. The amounts of air blown in were combined and introduced into sodium peroxide solution in order to determine in usual manner the chlorine dioxide formed. The temperature in the reaction vessel was 70 C. and in the purging vessel C. The acid concentration of the reaction liquid was about 3.6-4.0 N, the chlorate concentration was about 14 grams NaClO /liter in the reaction vessel and 3-4 grams per liter in the purging vessel.

In the course of 3 hours 689 grams N aclo corresponding to a yield of 85.5% calculated on the chlorate used, and 676 grams NaCl were obtained, The molar proportion 015010 in the gas producedwas 0.758:1.

Example 14 The experiment was carried out as described in Example 13, with the exception that the added sodium chloride solution was free from manganese sulfate. About 2.2-2.3 liters sodium chloride solution and about 0.8 liter sulfuric acid were required per hour. In the course of 3 hours 418.5 gramsNaClQ corresponding toa yield of 52.0% calculated on .the chlorate-used, and 1.142-,g11ams NaCl were obtained. The proportion Cl zClO in the producedgas was.2.11:1.

Example 15 In a reaction vessel 1.67 liters HCl (about 10 N); were added Within 5.84 hours to 5 liters of a sodium chlorate solution containing 138.5 grams NaClQ 351 grams CaCl and 2 grams MnCl AI I' Oper liter. Simultaneously, 1.1 cubic meter airnwere introduced per hour into the reaction solution having a temperature of 70. C. The gas mixture leaving the reaction vessel was introduced into aqueous sodium peroxide solution in. order-to determine in usual manner the chlorine dioxide.

554.4 gramsNaClO corresponding to a yield of 94.3%, calculated on the chlorate used, and 482.2 grams NaCl were obtained. 'The molar proportion (31,;010 in the produced gas was 0.672: 1.

Example 16 Theexpirement was carried out as described in Example 15, with the exception that the sodium chlorate.solu

tion used only contained 2 grams .MnCI AI-I O per liter 7.

and was free from calcium chloride. 2.63 liters HCl (about N) were requiredwhich Wereadded within-9 Example 17 A reaction vessel (capity about 8.0 liters), provided with overflow was charged perhourin doses with 343 cc of an aqueous chlorate solution of 554.5 grams NaClO per liter, 152 cc. H 80 of'78% strength and 208 cc. HCl (about 10 N), which contained per liter, 27.8 grams MnSO H O. .The chlorine dioxideformedwas diluted per hour with 1.5 cubic meters air. which were introduced into the liquid. The excess reaction. solution flowing off was purged in a-second vessel having a capacity ofabout 3 liters with 0.3 cubic meter air per hour and Was then ,discharged via a. siphon. The introduced amounts .ofeir were combined and conducted into sodium peroxide solution in order to determine in usual manner the chlorine dioxide formed. The temperature in the-reactionvessel was 69 C. and in the purging vessel 78-80 C. The acid concentration of the reaction liquidwas about 3.7-

4.0 N and the chlorate. concentration was about .14. grams NaClO liter in the reaction vessel and about -3-4 -;grams/ liter in the purging vessel. 7

Within 5 hours 737 gramsNaCIO correspondingto; a yield of 90.2% calculated on the chlorateused and .7106 grams NaCl were obtained. The molar proportion Cl :ClO in the produced gas was 0.751 1.

Example 518 The experiment was carried out as described in Example 17, with the exception that the added hydrochloric acid .was;free frornmanganesesulfate. .410 cc. hydrochloric lacid and. 162cc. sulfuric acid .wererequired per hour. In .thezco r epf SrhQur 5. r m NaC Oz. c e p jug to ;a y ield of 65.4%', and .1 .275 grams NaCl were obtained. 'Ihe-molar -proportion Cl :Cl O in the produced 3 was1. 387;2=1.

2 claim: V

,-.1.1.I amroee is n-th ma a tu ofch o ed d f y; redu inga eom'no udo theeroup con s of k me land alkalinetearth manlshlmate .w th hyd h o acid auaqu o .solution-th imp ore e wh h n- .si tsginrc rryiugzQut'the r act o atempe in h range from 0 11100?C.,;. ndin: heprese e sca y of the group consisting of Mn? ions in an amount between about 0.5 and about 1.5 g. per liter of solution, Ag+ ionseimanamount between' about"0.02 andabout 0.3 g. per liter .of .solution,.and combinations :thereof.

Z2.:-A.pr.ocess.as claimed in claim 1,.wherein chloride ions.in theforrn oflasalt selected from the. groupconsist- .ing of sodiumkhlorideand calcium chloride, are added in a proportion of 0.5. 1Q; mo1s .per moi of chlorate.

3. A process as defined in claim 1, wherein the reaction is carried out ata-temperaturebetween about 20 C. and :about C.

4. Ina-process-forthe'manufacture of chlorine dioxide by-reducinga compound of the group consisting of alkali --metal and alkaline-earth metal chlorates with hydrochloric acid in an aqueous-solution, theimprovement which consists in carrying out the reaction at a temperature in the range from O to C.. andin-the presence of a-catalyst consisting of Ag ions-in an amountof at least about-0.05

- g .-per liter of solution.

In a process for themanufact-ure of chlorine dioxide by reducing acor-npound of-the group consisting of alkali mletal-and alkalineear'th. metal chlor-ates with hydrochloric .--acid in an aqueous-solution, the improvement which consists in carrying out :t-hereaction at a temperature in the range from 0 to 1 00 C. and inthe-presence of a-catalyst consisting of a combination of Mn+ ions in an amount between about,0.5 and about 1.5 g. per liter of solution and Ag+ ions in an amount between about 0.02 and 0.3 g. per liter'of solution.

R'eferences Cited in the-fileof this patent 'UNITED STATES PATENTS Austria Jan. 10, -0 

1. IN A PROCESS FOR THE MANUFACTURE OF CHLORINE DIOXIDE BY REDUCING A COMPOUND OF THE GROUP CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL CHLORATES WITH HYDROCHLORIC ACID IN AN AQUEOUS SOLUTION, THE IMPROVEMENT WHICH CONSISTS IN CARRYING OUT THE REACTION AT A TEMPERATURE IN THE RANGE FROM 0 TO 100*C., AND IN THE PRESENCE OF A CATALYST OF THE GROUP CONSISTING OF MN+2 IONS IN AN AMOUNT BETWEEN ABOUT 0.5 AND ABOUT1.5 G. PER LITER OF SOLUTION, AG+ IONS IN AN AMOUNT BETWEEN ABOUT 0.02 AND ABOUT 0.3 G. PER LITER OF SOLUTION, AND COMBINATIONS THEREOF. 